As the castle’s front doors swung closed behind him, Jake glanced around the front hall. “Twilight?” he called out, a little surprised that the princess wasn't there to meet him. She was usually quick to greet him when he answered her invitations; Jake had thought of that as just typical pony friendliness, but in light of yesterday's events… it might have been because she had a crush on him. Jake was still processing that information.

There was a sharp noise behind Jake, and he felt a soft face nuzzling his butt. He instinctively jerked his body forward, and then whipped his body around to see Twilight Sparkle looking at him with a seductive smile.

“How was work, handsome?” asked Twilight, fluttering her eyelashes.

“A little weird,” he said. “Mares were looking at my ass all day… pointing it out to each other when they thought I wasn't looking, whispering about it and smiling…” he bit his lip awkwardly. “I kept worrying they would try to tackle and strip me like yesterday, but they just… looked.”

Twilight giggled, and did a giddy little stomp with her front hooves. “I love it!” she said. “My stallion has the butt that all the mares can't stop staring at!”

“Your… stallion?” asked Jake.

“Uh, yeah!” said Twilight - and then she vanished, and reappeared behind Jake. She started nuzzling his butt again, and this time he didn't move away from her. “Last night I licked your asshole for hours and made you cum dozens of times! The way I see it, that makes you mine!” She giggled, rubbing her about against the back of his pants. “Why? Don't you want to be my stallion, Jakey? Don't you like getting butt kisses from your favorite purple princess?”

“Well… yeah…” said Jake. Last night had been pretty incredible; thanks to Twilight’s magic, he literally had come dozens of time from getting his ass licked. “I just didn't know you were that serious about it. I mean, you're a magic princess and I'm just…”

“Just a one-of-a-kind man from another dimension,” said Twilight. “That makes you the rarest catch in Equestria! And on top of that, you've got that transcendently beautiful butt. I just wanna stare at it all the time… and give your cute little puckered butthole a hundred kisses every day…”

“Uh, wow,” said Jake. “Okay, I'll be your stallion. But… you're okay with other mares checking out my ass?”

“Well, they can't help it,” said Twilight. “Not as long as the lingering effects of that ‘Want It, Need It’ spell are still on your butt. Besides, I'm not a jealous mare, Jakey. You can show off your beautiful butt to as many mates as you want. If you feel like it, you can even let ‘em lick your asshole… as long as you come back here and tell me all about it!”

“Do you really think it'll be a long-term thing?” asked Jake. “Aren't the lingering effects going to wear off eventually?”

Twilight suddenly paused her nuzzling. “Well, now that you mention it… I'm not sure. I sure hope it is; I don't want to stop loving your butt, Jakey. Last night was the most fun I've ever had, and I always want to have your beautiful, kissable, lickable butt in my life. If it's not permanent, Jakey, I'll make it permanent.”

Jake was starting to get a little weirded out… but he was flattered by Twilight’s praise, and her enthusiasm was infectious. “Well, as long as mares are just looking at me, and not stampeding at me… I guess I could live with this.”

“Great!” said Twilight. “First things first… We need an experiment, Jakey, so we can figure out exactly how the effects work! Ooh, this’ll be fun… give me a little while to get things set up - when I come get you, Jakey, it'll be time to learn everything there is to know about your enchanted butt!”

“I've never seen this room before,” said Jake, regarding the pale blue, sterile-looking walls of the small rectangular room. “How far down are we? How far down does the castle go?”

“Pretty far down! The castle is sort of a magic tree,” said Twilight, “and the basement’s sort of a root system. I built my magic lab down here, out of the way of the castle-y stuff.”

“Huh, okay,” said Jake. “And what are we doing down here? What kind of test were you setting up for the past hour?”

“Just a modest scientific inquiry into what makes my boyfriend’s butt so sexy,” said Twilight. “I just needed to write up the test plan and call over a test subject.”

“Aren't I the test subject?”

“Yes and no,” said Twilight. “Here, just sit in this chair and wait while I get in the observation room.”

Twilight teleported a plain-looking, human-sized wooden chair into the room - then she vanished and reappeared on the other side of a window that occupied one long end of the rectangular room.

“Okay, I have equipment over here that suppresses and enhances magical fields,” said Twilight. When she spoke, her voice was projected into the room Jake was in; whether she was using magic or a microphone, Jake couldn't guess. “The ‘Want It, Need It’ spell on your butt has lost some of the potency it possessed yesterday, so I’m going to be testing it at its current power, then gradually raising its strength. Okay?”

“Uh, I guess?” said Jake. He wasn't sure that this test was necessary, but he trusted Twilight not to put him in any danger - and she was certainly excited about this. “So who's the ‘test subject’ you called over?”

Twilight, on the other side of the window, activated either a spell or a mechanism - and a door on the far side of the room opened up. “Hey Jake!” said a familiar voice, as a familiar pony trotted out of the adjacent room.

“Oh hey, Derpy!” said Jake, pivoting in his seat to face the gray pegasus. “I wasn't expecting, uh… well, anyway, hi!”

Derpy was something of a colleague to Jake; although she worked for the official Ponyville mail service and he worked for an independent courier service, they interacted pretty frequently. Jake found Derpy easy to talk to, and the two of them had spent the occasional lunch break together…

And Twilight knew about that, because Jake had told her. Could that have something to do with her decision to make Derpy her test subject?

“So what am I doing here?” asked Derpy. “Twilight just said it was important… and it'd be some kind of magic test?” She shrugged, and her wonky eye drifted to the side.

“It's nothing too taxing,” said Twilight, from behind the observation window. “Jake, could you stand up and turn around?” Lowering her voice, she mumbled to herself: “Spell power currently at approximately twenty-five percent…”

Jake braced himself, anticipating the reaction he'd get from Derpy. The mailmare, as it happened, was not one of the mares who'd chased him yesterday, nor had she seen his ass while he was out and about today. This would be her first exposure to the lingering “Want It, Need It” effect on his butt.

Jake stood and turned in a circle - and when he returned to his original orientation, he didn't see the same lustful smile he'd seen on the faces of the mares who'd seen his butt today. The “spell suppression” must have been doing its job…

But Derpy was affected, or so it seemed. A hot red flush began to develop on her gray cheeks, and she suddenly seemed to be finding it more difficult that usual to meet his eyes. She lowered her face, and when Jake tried to look her in the eyes, she lifted one wing to shield her face shyly.

“You all right?” asked Jake, bending his knees to bring himself down to her level.

“Yeah, J-Jake, I'm okay,” said Derpy, her voice wavering a bit. “It's just… the way you're looking at me, it's… you're making me blush, Jake…”

Jake was certain that he wasn't looking at Derpy any differently from usual. What had changed, he suspected, was that Derpy was perceiving him differently. Even at one-quarter strength, the spell was making Derpy think about Jake in a more romantic light. A more sexually confident mare might have started to flirt with him, but Derpy was naturally shy about such matters - and so she was hiding her face.

“Lowering suppression, spell power at fifty percent…” mumbled Twilight.

Derpy’s demeanor changed slightly: she peeked out from behind her wing, taking another look at Jake’s butt. “H-hey, Jake,” she said, standing a little taller, “you should come by the post office on your lunch break tomorrow. It's, uh, been a while, right? We can grab sandwiches, and you can, uh…” she took a heavy breath. “…you can sit on my desk. Just…” she took another heavy breath, and her wings started to rise. “Just sit your butt right on my desk, right where I do my work…”

Jake laughed nervously. There was that now-familiar effect: the ass obsession that mares who saw his butt all developed “yeah, we could grab lunch…” he said.

“Spell power seventy five percent…” mumbled Twilight

“Actually,” said Derpy, “lunchtime might be busy for me tomorrow. How about dinner? I'm a good cook, Jake, you can come over and I'll cook you a nice dinner, and I can show you my bedroom…”

Derpy’s wonky eye spun, as if in a panic, and she fluttered her wings slightly. “My house!” said Derpy. “I mean I can show you my house, you can see all the rooms if you want! The bedroom, the bathroom… you'd like my bathtub, Jake, you could fit a human in my bathtub and still have room leftover for a pony to get in with him!” Her blush deepened as she realized what she'd said. “I mean, I mean…” she stammered, her knees quivering.

“Dinner sounds nice!” said Jake, “but I might have to check with, uh… my schedule… to see if I can.” Derpy seemed to calm down slightly, but she was still shaking - and Jake, more or less on instinct, put his hand on the crown of her head, running his fingers through her golden hair and scratching gently behind her ears.

“Mmmhhh,” moaned Derpy, leaning her head into Jake’s hand. “Jake, that feels good… I want to repay the favor, Jake, I know a way to touch you that you'll really like…”

Derpy ducked her head and scampered around Jake, until she was facing his butt - and then she buried her face in his ass, nuzzling his cheeks and sighing happily. “Does this feel good, Jakey?” she asked. “These cheeks are so soft, I bet it feels nice when I touch them…”

“Spell power at normal strength,” muttered Twilight.

“Jakey, I've always wondered…” said Derpy, rearing back and putting her forehooves on his cheeks, “why do you wear clothes all the time? It must get hot and uncomfortable, covering yourself up like that.” She bent her wings forward, digging them into the waistline of his pants. “You should be more like us ponies are, and not cover yourself up… I bet some ponies want to see all of you, Jakey…”

Jake tried to lunge forward, away from the mare who was trying to forcibly pull down his pants. But he couldn't move his body forward - when he tried, his body bounced lightly off a purple shimmer in the air.

“Your butt is such a handsome shape,” said Derpy, “I just want to see it. I just want to touch it with my face, and dig my nose between your cheeks, and kiss your butthole a million times…” with a forceful tug, she brought Jake's pants down to the floor, and she stumbled back. Her eyes spinning, she stared at the back of Jake's boxer shorts, drool glistening on her lips.

Twilight Sparkle’s voice echoed through the small room. “Derpy,” she said, “can you describe what you're feeling right now?”

“I, uh, I need to see Jake’s butt,” said Derpy, sounding almost hypnotized. “It's beautiful. I'm in love with it, I need to be closer to it, I have to kiss it and lick it or I'll explode…” she closed her teeth on the fabric of Jake’s boxers and tugged, tearing them by the seams. As soon as she saw Jake’s bare ass, her legs began to tremble and fluid dropped from her glistening pussy. “Ohhh Jake,” she sighed.

“Do you want to worship Jake’s asshole, Derpy?” asked Twilight. “Do you want to bury your face in his asscheeks and never come out?”

“Yes, I want his butt so much, I have to have it...” said Derpy. She plunged her face into his asscrack, nuzzling his cheeks as she dug herself deeper.

“Well, here's the thing,” said Twilight. “Jake’s butt already belongs to me. Last night I kissed his perfect butt and licked his asshole and made him cum dozens of times. I ate his ass all night long, and that makes him mine. You're a kind and honest mare, Derpy… you wouldn't try and steal a princess’ boyfriend, would you?”

Derpy paused and stepped back, shaking her head in confusion. “Uh… I didn't know…” she said, although her eyes were still glued to Jake’s ass. “I don't want to come between you, I don't… want to hurt anyone…”

“Spell power at two hundred percent,” said Twilight.

Derpy lunged at Jake’s butt, knocking him to the floor. “I don't care,” she groaned, licking passionately at Jake’s asscheeks. “It's too good, I have to have Jakey’s ass, it has to be mine…” she dug her face between Jake’s cheeks again, and this time her warm, wet tongue dragged across his puckered asshole. Jake shuddered in surprise and pleasure, his stiff cock jumping.

“Yes, yes, this is very good data,” said Twilight. Jake thought he could hear another sound coming through from the control room, though - a schlick, schlick sound like a mare’s hood stroking her own pussy. “At two hundred percent, subject’s moral inhibitions were overridden… she proceeded to… mmm… tackle Jakey and lick his tight little butthole, pleasuring his ass with her soft tongue… even after being told that Jakey was mine, she couldn't stop herself from tonguing his perfect, tasty little asshole, right in front of me… oooh… while I'm watching…”

It became pretty clear to Jake that Twilight’s reasons for running this test weren't purely scientific. She’d set up a test where another mare would be exposed to the “Want It, Need It” spell on his butt, then increased the power of the spell until it would be impossible for Derpy to resist. And now she was touching herself, narrating the scene as another mare had her way with her boyfriend. Jake had assumed that Twilight wanted an exclusive relationship with him, the way most human women would… but Twilight Sparkle wanted to watch other mares with their snouts deep in Jake’s buttcrack, licking his asshole, helpless against their desire.

“Need more data,” panted Twilight, between heavy breaths and wet schlicking sounds. “When does the spell overpower a mare's inhibitions? When does desire become stronger than moral considerations? Might… vary from pony to pony… need to set up tests with… Pinkie… Applejack… Rainbow Dash, maybe… Celestia and Luna… see if alicorns are affected differently…”

Jake was increasingly overwhelmed by the passionate rimming that Derpy was giving him… but he could still hear Twilight talking to herself, stimulating her arousal with fantasies. A revolving cast of beautiful mares, driven mad with desire at the sight of Jake’s butt,

“Mmmph… more data… deeper investigation,” breathed Twilight. “Three hundred percent…”

Jake felt Derpy’s mouth pushing out a low, muffled moan that grew into a full-throated cry. Her hooves, planted on his buttcheeks to pin his body down, began to shake. Her whole body was quaking as she cried out nonstop, her tongue pressing harder into Jake’s asshole as she came.

“Ooh, ooh, excellent data,” groaned Twilight. “So good, the data’s so fuckin’ good…” she was panting, her head bobbing beyond the control room’s window, still working her good up and down her sipping pussy lips. “Spontaneous orgasm at… three hundred percent… very important to test this with additional mares… make sure Jakey’s butt gets lots and lots of love…”

Jake was getting close to climax himself; his cock was throbbing, leaking pre onto the floor of the testing room. Derpy’s orgasm wasn't stopping her from rimming him, either - she was still deep inside his asscrack, tonguing his pucker with absolute dedication. Jake felt Derpy's hooves shaking less, growing steadier as her orgasm came to an end… but not four seconds later, her body began to quiver again, and her moans grew in volume as her body was hit with another climax, pounding her in waves. But her tongue never left Jake’s asshole; she needed his butt, she had a thirst for his asshole that no amount of lapping could ever satisfy.

And Jake, relentlessly pleasured by Derpy’s tongue, finally came. His cock erupted forcefully, splattering the floor beneath him, firing off rapid spurts of cum while he wriggled helplessly underneath Derpy. And Derpy - of course - didn’t relent; her tongue was still circling, pressing at his pucker.

“Ah, Jakey just came,” said Twilight. “I’ll need to enchant his cock again, so he can keep cumming as long as Derpy eats out his asshole. I have to make sure my Jakey is able to have fun… or else what kind of girlfriend would I be?” There was a tingling warmth around Jake’s cock, and he felt himself getting hard again. The post-orgasmic feeling faded, and Jake felt ready to cum all over again.

“And as for Derpy, our subject,” said Twilight, “Three hundred percent spell power gives her multiple… perhaps continuous… spontaneous climaxes. The enchantment has taken on fascinating new behavior in its liquid form. Not only has it attached itself permanently to Jakey’s butt, it has adapted itself to create irresistible sexual attraction. And with increased power, it… creates overwhelming pleasure… stimulating the mare’s pussy to climax…” She panted heavily, close to orgasm, stroking herself furiously. “Should I push the spell’s power higher? Four hundred percent could be… illuminating…” For a moment, she seemed to consider the question as she touched herself. “No,” she finally concluded, “not ethical to take it further, but very tempting…”

Jake felt his cock throbbing again, building up to another climax. “Jakey,” gasped Twilight, “I’m monitoring your body, and I can see you’re about to cum again. Do you want me to cum with you? Should we cum together? Mmm, how romantic…”

Jake couldn’t respond with more than a grunt - but Twilight wasn’t really waiting for him to respond. She stroked herself harder, sinking the side of her hoof deep into the wet folds of her marehood, determined to finish herself off.

And Derpy beat them both to the finish line, shaking and groaning with her third climax. Jake could only imagine what Derpy was going through; the magic - at three times the strength it had yesterday - had overpowered her mind, turning her into a ravenous, ass-eating sexual beast. How much worse would yesterday’s chaos have been, if the spell had been this powerful? Bon Bon would have torn Jake’s pants off and rimmed him right where she found him, climaxing endlessly as she pleasured his pucker. And when other mares came along… a riot would surely have engulfed Ponyville. A mob of mares, driven mad by lust, salivating at the thought of Jake’s butt, fighting for the right to own it…

Jake told himself that he didn’t want this, that it was strange to be the object of so many mares’ desires. But he couldn’t deny that the thought of it was exciting - all these mares lusting for his ass, climbing over each other for a chance to worship it. Even when the spell’s power was diminished, Jake could effortlessly seduce any mare he wanted, and she would kiss his asscheeks and rim his pucker until he shot his load…

Jake’s fantasies drove him over the edge again - and Twilight, who had been watching him closely, brought herself to climax at the same moment. She cried out, and her sound-projection magic filled the testing room with her voice. “Jakey,” she gasped, “I’m coming! We’re coming together! Ahh… it must feel so good, Jakey… Derpy’s licking your butthole while your long hard cock is shooting a big load of cum…” She staggered back, falling on her rump as her cunt throbbed in climax. “Don’t forget you’re mine, Jakey,” she groaned. “Some other mare is licking your butthole, but you’re still mine… no matter how many other mares I give you to, Jakey, you belong to Twilight Sparkle…”

Twilight’s groans faded into a sigh, and she slumped to the floor. Jake, too, was done with his orgasm, having shot his second load onto the floor beside his first. But Derpy was tireless - utterly consumed by lust, she rimmed Jake’s butthole with undiminished vigor and brought herself to a fourth climax.

“Oh my,” sighed Twilight, standing herself back up. “I’ve put Derpy through a lot, haven’t I? I guess she’s earned a break, since she’s given us a lot of good data… I’m sure she’s having the time of her life back there, but I should probably dial the spell power back to where it was before…”

Twilight’s magic shoved Derpy away from Jake’s butt - and when Jake turned to look at her, her glazed-over eyes gradually brightened. “Oh, wow,” Derpy murmured, “that was like really intense, Jake… sorry if it was too much, I just had to get in that butt…” She slowly bent her knees and settled on the ground - not sleeping, but resting her exhausted body. Now that the “Want It, Need It” spell wasn’t making her senselessly lustful, she didn’t have the energy to remain standing - much less to continue eating out Jake’s ass.

The door to the testing room opened, and Twilight stepped inside, looking just a little bit sheepish. “I may have taken things a little farther than I should have,” she said, “But it’s just so easy to let myself get carried away.” She trotted over to Jake - who was still face-down on the floor - and gave one buttcheek a quick kiss. “If you’ll let me, I think I know a way to make it up to you…”